X THE BUOYANCY OF SEEDS AND SEEDVESSELS 91 



that are known to be dispersed by the ocean-currents will float 

 well in fresh water is shown in the constant occurrence in the 

 floating drift of Fijian estuaries, where the water may be quite 

 fresh or brackish, of the seeds and fruits of plants like Cerbera 

 odollam, Clerodendron inerme, Entada scandens, Heritiera littor- 

 alis, Ipomea pes caprae, Morinda citrifolia, Mucuna, Vigna lutea, 

 &c. In the same way I noticed afloat in the Guayaquil River 

 in Ecuador, when the water was quite fresh, seeds and fruits 

 characteristic of the sea-drift, such as those of Anona paludosa 

 (seeds), Entada scandens, Ipomea, Mucuna, Vigna, &c. ; and 

 when we supplement observation with experiment, as for instance 

 in the case of Anona paludosa, we find that they will float 

 equally long in fresh and sea-water. 



The same rule prevails with most of the buoyant seeds 

 and seedvessels of plants' of the British flora — seeds and fruits, 

 as I may remind the reader, that are mostly to be found in 

 river and pond drift. I am not able to distinguish any differ- 

 ence of importance in the results of the separate fresh-water 

 and sea-water experiments. Thus with the seeds or seedvessels 

 of Bidens cernua, several species of Carex, Galium palustre, 

 Iris pseudacorus, Lycopus europaeus. Ranunculus repens, and 

 numerous others, the difference after a flotation of many months 

 was but slight. If the results of the separate experiments were 

 to be compared, there would be at least ninety afloat in fresh 

 water for every hundred afloat in sea-water ; and if at the end 

 of a sea-water experiment, whether occupying three, six, or 

 twelve months, the seed or fruits were to be placed in fresh 

 water, quite nine-tenths and sometimes more would remain afloat. 

 A striking illustration of the principle that the excess in density 

 of sea-water, as compared with fresh water, adds but little to 

 the floating capacity of seeds is to be found in the results 

 given in Note 41 of simultaneous experiments made some years 

 since by Mr. Millett and myself at Marazion and in London 

 on the seeds of Convolvulus soldanella. 



(D) In their relation, therefore, to the density of fresh water 

 and sea-water, most seeds and seedvessels may be placed in two 

 principal classes, the first including qtiite four fifths of the total, 

 where they are imich heavier than sea-water, and the second com- 

 prising most of the remainder, where they are 7nucii ligJiter than 

 fresh water. 



(E) It would be surprising, however, if there were not some 

 seeds or seedvessels that come between these two extreme 



